1. Field of the Invention
The present invention relates to capacitor manufacturing technology field and, more particular, to a method of measuring surface area variation rate of a polysiticon film having hemispherical grains (HSG), and capacitance measuring method and apparatus by the same.
2. Information Disclosure Statement
High integration of semiconductor device is accelerated according to a development of technology. In particular, in case of DRAM memory device the high integration is intensified, and to form the high integration DRAM memory device, the number of capacitors to be integrated per unit area is increased and accordingly the area occupied by unit capacitor is decreased, therefore it is not easy to secure the capacitance of magnitude which can satisfy a drive characteristics of the device.
As solutions of such problems, various attempt have been made to increase the surface area by forming a capacitor of 3-Dimensional structure to secure a desired sufficient capacitance with small area.
As one of such methods, there is a method of increasing the surface area of capacitor by forming a HSG film on the surface of silicon film.
FIGS. 1a and 1b are sectional views showing an example of a conventional method of forming a HSG film on the surface of silicon film, which schematically show the formation of a spherical shape silicon grain or a hemispherical shape silicon grain 12 on the surface of silicon film 11 by using a gas of SiH.sub.4 or Si.sub.2 H.sub.6.
FIGS. 2a to 2c are sectional views showing other conventional example of forming the a HSG film on the surface of silicon film, which schematically show the formation of a spherical shape silicon grain or a hemispherical shape silicon grain 23 by depositing an amorphous silicon film 21 to be an electrode, absorbing a silicon atom 22 into the surface of amorphous silicon film 21, and moving silicon atom included in the amorphous silicon film 21 around the silicon atom 22 absorbed into the surface.
The capacitance `C` is proportional to the area `A` of capacitor as shown in Equation 1 below. In Equation 1, dielectric constant of a dielectric material is `.di-elect cons.` and thickness of the dielectric material is `d` and surface area of capacitor is `A`. ##EQU1##
Therefore, at the time of forming the dielectric material of same material to an identical height, since the capacitance of capacitor is decided by the area `A` of capacitor, it is very important to precisely monitor the surface area in case of forming the HSG film on the surface of silicon film as described above.
A conventional method of monitoring the surface of film is to irradiate a light having a predetermined wavelength on the surface of film, measure a phase difference of light, intensity of light, polarization variation rate, etc. of the light reflected from the surface of film, be provided with information on the surface of film such as height of film, reflection rate of film, deflection rate of film and porosity ratio of film, and to indirectly measure the surface area of film based on such information.
FIGS. 3a and 3b are a schematic view to illustrate a conventional method of monitoring the surface of film. As shown in FIG. 3a, the light incident from a light source 100 arrives at a semiconductor film 50 via a first lens 31, a reflection mirror 41 and a second lens 32, then is reflected at the semiconductor film 50, and is input to a signal processor 200 via the second lens 32, the reflection mirror 41, a third lens 33, a light polarizer 300 and a light collector 42. However, in the process of collecting the information on the film as described above, the information not only on the surface of film 50 but also on a lower stack film are transmitted. That is, taking as an example an incident light i incident toward the film 50 as shown in FIG. 3b, a light r.sub.1 reflected at an indentation surface of the film 50, a light r.sub.2 reflected at an interface between the indentation surface and a lower film and a light r.sub.3 reflected at bottom surface of the lower film are together detected.
Therefore, the conventional method of indirectly measuring the area by irradiating the light having the predetermined wavelength to the surface of film and by measuring the phase difference, intensity and polarization variation rate, etc. of the light reflected from the surface of film has problems in that it has a significantly degraded precession and, furthermore, cannot monitor the result of process since it cannot obtain precise area.